This invention relates generally to instrument calibrators and more particularly to an instrument calibrator combined with a hand held personal computer, preferably a personal digital assistant (PDA) having graphical input and output, and a stylus for user interaction with the graphical interface.
The use of calibrators for regularly verifying the accuracy of instruments used in process automation and other applications has been known for some time. Manual calibrators provide a signal source of traceable accuracy and, optionally, measuring capabilities. The most basic calibration method includes the steps of connecting the verifiable source to the instrument or device being calibrated and noting the reading or action produced by the instrument in response to the source. If the response or reading is within predetermined acceptable limits, the reading is simply recorded along with the date and additional information such as the operator""s name, and identification code for the calibrator, the identity of the device being calibrated and similar information. If the instrument reading is outside acceptable limits, remedial steps are taken to recalibrate the instrument or device.
For example, process instrumentation commonly utilizes a current control signal in the range of 4 to 20 milliamps. A device such as a valve is connected in an open or closed loop control system that controls the position of the valve. Conventionally, a 4 milliamp signal completely closes the valve while a 20 milliamp signal completely opens the valve or vice versa. A metering device such as a current meter can be connected to the valve to monitor the magnitude of the current signal applied to the valve. Alternatively, a recorder such as a chart record may be connected to record the position of the valve during a process. Both the accuracy of the recording instrument and the response of the valve to the control signal must be periodically tested to insure proper operation of the process.
Calibrators that provide a traceable verifiable signal in the 4 to 20 milliamp range are widely employed for this purpose.
It is desirable to retain the information associated with the calibration of process instrumentation for some time after the calibration has been carried out so that the performance of the instruments can be monitored. Therefore, it has been common to keep written records or enter data taken by calibration technicians into a database for later retrieval, for the analysis of trends and for other purposes including verifying that the necessary periodic calibrations have been in fact carried out.
For the most part, data related to calibration has been recorded manually on forms provided for that purpose, and thereafter entered into a database, if required, usually maintained on a personal computer, directly from the forms. This approach is time consuming, labor intensive, and may lead to errors unless great care is taken in the recording of the data, the entry of the data into a computer, and the verification of the entered data.
To avoid some of these time consuming, error prone manual steps, documenting calibrators have been introduced. Documenting calibrators automate one or more of the steps previously performed manually. Documenting calibrators typically provide both a traceable source and measurement capability in a single unit. Documenting calibrators typically include memory for recording measured data to eliminate the need for manually entering the data on a form. Some documenting calibrators provide multiple functions in a single unit. For example, a documenting calibrator may provide a traceable voltage and current sources as well as variable frequency sources. Simulated thermocouple output sources may also be provided.
While documenting calibrators provide a number of advantages over more basic calibrators, they are presently quite expensive and even more important, require extensive set up before they can be used. Information concerning the device or instrument to be calibrated must be entered into the documenting calibrator before a calibration procedure can be carried out. Existing documenting calibrators require that information concerning each instrument to be calibrated, including the identification of the instrument, its location, the procedure for making the calibration, and the identity of the calibrator be downloaded to the documenting calibrator each time a new instrument or device is added to those already calibrated. This process is inconvenient and time consuming, and requires that the documenting calibrator be physically connected to a stand alone computer each time a new instrument/device is added. Among the data that must be downloaded to the documenting calibrator are tag IDs and associated calibration procedures.
There is a need for an instrument/process calibrator that overcomes the disadvantages of manual calibrators, and at the same time increases the convenience of documenting calibrators by making them easier to use and more versatile.
It is an object of this invention to provide an instrument or process calibrator that uses a general purpose computer, preferably a personal digital assistant (PDA) or similar device to provide the human interface to the calibrator, to store information relating to the calibration itself, so as to automate, to a greater or lesser extent, the calibration process, and to store the results of the calibration.
It is another object of this invention to provide a general purpose computer, preferably a personal digital assistant, that is configured to both store information concerning an instrument or process to be calibrated, and provide for the entry and storage of data taken during the calibration process.
It is a further object of this invention to provide an instrument/process calibrator that uses a portable general purpose computer to temporarily store calibration information and results during the calibration process, and to upload that information to a database on another computer for long term storage and analysis.
Briefly stated, and in accordance with a presently preferred embodiment of the invention, an instrument or process calibrator includes a housing, a traceable, controllable calibration source in the housing, the calibration source including memory for storing identifying information about the calibration source, a data connector coupled to the calibration source, a removable hand held computer preferably a PDA, attached to the housing, and connected to the data connector, the computer including user input means for receiving a control input user for controlling the calibration source, and output means, preferably graphical output means for displaying the identifying information and calibration results to the user.
In accordance with another aspect of the invention, the hand held computer includes an input device for receiving calibration data from a user and memory for storing the calibration data.
In accordance with another aspect of the invention, a hand held computer includes an output circuit for transferring the stored calibration data and the identifying information to another computer.
In accordance with another aspect of the invention, the hand held computer or PDA includes a touch screen for receiving data and control inputs from the user.
The PDA calibrator of this invention utilizes a common user interface to a family of calibrators. By providing a familiar interface, different calibrators may be used by a previously trained technician without the need for extensive additional training. The use of a consistent familiar graphical interface eliminates the usual array of buttons and knobs that traditional hand held calibrators have required for operation. The common interface permits operators to be trained quickly, and eliminates the need for retraining for new calibrator devices. The ability to transfer data from the PDA to a host computer and back provides a fast and simple link to share data and files with the host computer. The host computer is not required, however, as the software resident in the PDA can operate on a stand alone basis if required.
The calibrators of this invention include both source and read functions with accuracies equal to or exceeding existing calibrators. The calibrators of this invention are low cost alternatives to single purpose documenting calibrators in current use. By eliminating the need to transfer information relating to new instruments from a host computer to a documenting calibrator, the PDA calibrator of this invention provides unprecedented versatility at low cost. The PDA calibrators can operate on a stand alone basis to allow a calibration technician to use the PDA and its accompanying software if the field to build a device data base with each new calibration, thereby eliminating the time consuming need to prepopulate a data base from a host computer prior to performing calibrations.
The PDA calibrator is adapted to integrate easily with existing maintenance practices and systems.
The PDA calibrator of this invention allows calibration data to be gathered and shared much more easily than heretofore possible. A calibration technician using the PDA calibrator on the plant floor, can gather, evaluate and share information company wide and even worldwide much more efficiently than has been heretofore possible.
A PDA calibrator in accordance with this invention can be used by a technician to calibrate a new instrument by entering information on the instrument or device to be calibrated into the PDA using the PDA graphical user interface and a pen or stylus. If information concerning the device or instrument already exists and and can be easily retrieved from data stored on the PDA.
While the preferred embodiment of the invention utilizes a calibrator base to perform the calibration, thereby allowing data to be read directly from the calibrator, data can be entered manually on the PDA if desired, for example if no suitable calibrator base is available. The PDA software operates on a stand alone basis that can be used either with or without a calibrator attached to the PDA. This allows non-electronic calibrations that are normally made manually, such as scales and gas analyzers to be performed, using the PDA calibrator.
As calibrations are completed, non-automatically retrieved calibration information is entered on the PDA, and the results of the calibration are uploaded to the host computer via a hot sync data transfer function. This creates a permanent electronic record and allows the user to create a variety of records including certificates of calibration if desired. A variety of desk top applications already in existence can be easily interfaced with the PDA calibrator.
By utilizing existing PDAs, technicians using the PDA calibrators have access to all other functions of the PDA, which allow them to schedule the work and appointments, download compatible third party software such as conversion and electrical calculators and look up tables, all enhancing their overall productivity.